1. Field of the Invention
The present invention relates to an illumination device for illuminating an object to be illuminated and an exposure apparatus using the illumination device and, more particularly, to an illumination device for illuminating a reticle, on which a pattern to be transferred is formed, in an exposure apparatus for manufacturing, e.g., a semiconductor element, a liquid crystal display element, or the like, and a projection exposure apparatus using the illumination device.
2. Related Background Art
For example, in the manufacture of a semiconductor element, a liquid crystal display element, or the like in a photolithography process, a projection exposure apparatus for transferring a pattern formed on a photomask or a reticle (a "reticle" will be used as an example hereinafter) onto a wafer (or a glass plate, or the like) via a projection optical system under predetermined illumination light, a proximity type exposure apparatus for directly transferring a pattern on a reticle onto a wafer arranged in the vicinity of the reticle, or the like is used. Such an exposure apparatus (to be referred to as a "semiconductor exposure apparatus" hereinafter) uses an illumination device for illuminating a predetermined region on a reticle at an illuminance as uniformly as possible using an optical integrator to reduce any nonuniformity of exposure amount on a photosensitive substrate. In this case, the numerical aperture (N.A.) of illumination light is set by the diameter of an illumination system aperture stop, which is arranged at the position of a light source image formed by the optical integrator.
As a conventional illuminance device of this type, a device which uses illumination light with a fixed numerical aperture is mainly used. In recent years, however, as a super-resolution technique such as a so-called variable-shape light source method (e.g., see Japanese Patent Laid-Open No. 4-101148), a phase shift mask method (e.g., see Japanese Patent Publication No. 62-50811), or the like has been developed, such a technique cannot be utilized while the numerical aperture is fixed. Recently, a mechanism in which an illumination system aperture stop for determining the numerical aperture has a continuously variable diameter, a mechanism in which stops with various patterns can be selectively set in a revolver method, or the like is adopted.